"I definitely have my regular places. Or I just eat at home for the security and to avoid the hassle," she said.

The study also looked at the knowledge and training of gluten-free food preparation among staff, with only 10 per cent found to have good knowledge of the food standards code.

Dr Tye-Din said food outlets needed better training for staff, warning the problem was likely to be worse in rural and regional areas.

"This is a snapshot of inner-city Melbourne. This is probably a conservative estimate," he said.

"This is not a lifestyle choice. There are people whose health really depends on this diet."

Editor's note (29/05/18): This report was originally published with a photograph of products baked by Munja Bakehouse Pty Ltd, including the "FNG Bar" and the "Not Just Another Seedy Bar". The ABC wishes to clarify that the products depicted in the photograph are gluten-free. The ABC apologises to Munja Bakehouse.